Curing processes using di-(2-methylbenzoyl)peroxide

ABSTRACT

Improved processes for curing unsaturated polyester resin compositions by employing di-(2-methylbenzoyl) peroxide as a curing catalyst.

United States Patent Field'of Search ..260/ 861, 864

Groepper 1 Sept 5, 1972 541 CURING PROCESSES USING DI-(2- [56]References Cited METHYLBENZOYL)PEROXIDE OTHER PUBLICATIONS [72]Inventor: Jurg n r pp Gunzburg. r- Blomquist, et al.; J. Am. Chm. Soc.73, 3883- 3888 y 1951 j v [73] Assignee: Pennwalt Corporation, Philadel-Cooper h S 1951 3l06'3ll3 phialpa" Pr E '1 M l G ld t imary xaminerevino stein [221 Flled- Attorney-Carl A. Hechmer,'-Jr. and William D. 21.Appl.No.: 103,283- Mitchell 3 a v 52 U.S.Cl .260/861, 260/864 v [571'ABSTRACT [51] Int. Cl. ..'...C08f 21/00 I r v d processes for caringunsaturated polyester resin compositions by employingdi-(Z-methylbnzoyl) peroxide as a curing catalyst.

3 Claims, No Drawings I CURING PROCESSES USING DI-(2-METHYLBENZOYDPEROXIDE BACKGROUND OF THE INVENTION This invention relatesto-the use of di-( 2-methylbenzoyl) peroxide as a curing catalyst (freeradical initiator) in unsaturated polyester resin compositions.

While dibenzoyl peroxide is a standard peroxide catalyst usedindustrially for curing of unsaturated polyester resins, it has severaldisadvantageous properties which have prompted research on better curingcatalysts. For example, since the cure times of dibenzoyl peroxide arehigh, lower temperature peroxides have been tried. I-Iowever, most lowtemperature peroxides are thermally unstable and decompose violentlywhen allowed to warm to room temperature. Further, dibenzoyl peroxidedissolves at a relatively slow rate in unsaturated polyester resins,thereby further increasing the overall resin cure time cycle. Thirdly,dibenzoyl peroxide usually results in a cured resin having a lightyellow or orange-yellow color in unpromoted (unaccelerated) and promotedsystems, respectively. In seeking improved curing catalysts, it is alsoimportant that the catalyzed resin have a Tank or Pot Life (seeprocedure described in the Proceedings of the 24th Annual TechnicalConference, 1969 Reinforced Plastics/Composites Division, The Society ofthe Plastics Industry, Inc., Resin Committee, Suggested SPI ProcedureStability of Catalyzed Polyester Resin Tank Life, page 2) of at least 24hours. The Pot Life of a peroxide is defined as the time for a 1 percentsolution of the peroxide in the unsaturated polyester resin to gel, getstringy or solidify when held at 25 C.

BRIEF SUMMARY OF THE INVENTION This invention concerns, in a process forcuring polyester resin compositions with free radical initiators (curingagents), the improvement of employing as said initiator, an initiatingamount of di-(Z-methylbenzoyl) peroxide.

DETAILED DESCRIPTION OF INVENTION It has now been discovered thatdi-(2-methylbenzoyl) peroxide is stable to decomposition at roomtemperatures, gives rapid cures of unsaturated polyester resins whichhave less color (in accelerated and unaccelerated cures) than resinscomparably cured by dibenzoyl peroxide, dissolves rapidly in the uncuredresin composition and has a Pot Life of several days.

Unsaturated polyesters which are used as the one component of thepolyester resin compositions according to the present invention are, forinstance, polyesters as they are obtained by esterifying preferablyethyleni cally unsaturated dior polycarboxylic acid or their anhydrides,such as maleic acid, fumaric acid, glutaconic acid, itaconic acid,mesaconic acid, citraconic acid, allyl malonic acid, allyl succinicacid, and others, with saturated or unsaturated polyalcohols such asethylene glycol; diethylene glycol (2,2'-dihydroxy ethyl ether);

least partly, by saturated carboxylic acids such as adipic acid,succinic acid, sebacic acid, and others, or by aromatic dicarboxylicacids, such as phthalic acid, tetrahydrophthalic acid, and others andtheir anhydrides such-as phthalic anhydride. Theacids used as well asthe alcohols employed may be substituted by other substituents,preferably by halogen. Examples of suitable halogenated acids are, forinstance, tetrachloro phthalic acid; 1,4, 5, 6, 7, 7-hexachloro bicyclo(2,2,1) heptene (5)-2',3-dicarboxylic acid, and others, or theiranhydrides.

The other component of the unsaturated polyester resin compositions areunsaturated monomers,

5 preferably ethylenically unsaturated monomers such as V propyleneglycol (a polyalcohol), maleic anhydride triethylene glycol (ethyleneglycol bis-(2-hydroxy ethyl ether); propanediol-1,2; butanediol-l,3;2,2-dimethyl propanediol-l,3; butene (2)-diol-1,4, glycerol,pentaerythritol, mannitol, and others. Mixtures of such acids and/oralcohols may also be used. The unsaturated dior polycarboxylic acids maybe replaced, at

(anhydride of an unsaturated dicarboxylic acid) and phthalic anhydride(anhydride of an aromatic dicarboylic acid) and as the monomer componentstyrene.

Peroxide levels of about 0.05 to 5.0 percent or more by weight of thecurable resin composition can be used, preferably 0.1 to 2.0 percent.Curing temperatures of from about room temperature (20-25 C.) to aboutC. are normally employed, accelerators (such as N,N-dimethylaniline andother dialkylanilines or N,N- dimethyl p-toluidine) normally being addedwhen curing at the lower temperatures to improve efficiency.

. EXAMPLES The following examples illustrate the invention but are notin limitation thereof. Parts are by weight unless otherwise indicated.

Example I 82 C. SPI Exotherms of Di-( 2-methylbenzoyl) Peroxide Curecharacteristics of di-(Z-methylbenzoyl) peroxide and dibenzoyl peroxidewere determined in an unsaturated polyester resin composition (a mixtureof an unsaturated polyester and styrene monomer).

The unsaturated polyester was an alkyd resin Acid No. of 45-50) made byesterifying the following components:

Components Quantity Maleic anhydride 1.0 mole Phthalic anhydride 1.0mole Propylene glycol 2.2 moles Inhibitor added (hydroquinone) 0.013%

Seven 7) parts by weight of the alkyd resin was diluted with three (3)parts by weight of monomeric styrene, the resulting composition having aspecific gravity of 1.14 and a viscosity (Brookfield No. 2 at 20 rpm.)of 13.08 poise.

Curing Procedure: Gelation and cure characteristics of the initiators inthe above resin were determined using the standard SPI Exothermprocedure (SPI Procedure for Running Exotherm Curves Polyester Resins,published in the Preprint of the 16th Annual Conference 00072ReinforcedPlastics Division Society of the Plastics Industry, lnc., February 1961Using this procedure at 82 C. (180 F.), di-(2- methylbenzoyl) peroxideand dibenzoyl peroxide were employed, at peroxide levels equivalent inactive oxygcn content to 1 percent by weight of dibenzoyl peroxide(based on weight of curable resin), to cure the resin composition. TheSPI Exotherm data and color of the resulting cured resins are shown inTable I:

TABLE I Gel Cure Peak Peroxide (Min.) (Min.) (l'1.) Barcol ColorDi-(Z-methylbenzoyl) 0.3 1.1 382 45 Almost colorless Dibenzoyl 3.7 5.4402 45 Slight yellow (1 color increases in the order: colorless almostcolorless slight yellow yellow yellow-orange.)

The Tank Life of the unsaturated polyester resin composition withdi-(Z-methylbenzoyl) peroxide added, determined by the Suggested SPIProcedure described hereinabove at 25 C., was 5 days.

EXAMPLE Il ROOM TEMPERATURE Accelerated Cures The procedure of Example Iwas repeated, except that 0.1 percent by weight of N,N-dimethylanilinewas added to the catalyzed resin as an accelerator and the resin wasallowed to cure at room temperature (25 C.), with the following results:

TABLE II Gel Cure Peak Peroxide (Min.) (Min.) (F.) ColorDi-(Z-methylbenzoyl) 8.5 14.8 3l5 Yellow Dibenzoyl 15.0 21.5 315Orange-yellow EXAMPLE III RATES OF DISSOLUTION IN RESIN 0.5 gram ofdibenzoyl peroxide (granular) and 0.5 gram of di-(Z-methylbenzoyl)peroxide (granular) were added individually to 50 grams of the resincomposition described in Example I. At 25 C., the resulting mixtureswere mechanically stirred and the times for complete dissolution of theperoxides in the resin noted as tabulated below;

TABLE III Dissolution Time Peroxide (minutes) Di-(Z-methylbenzoyl lessthan one minute Dibenzoyl 20 minutes EXAMPLE IV THERMAL STABILITY 25gram samples of di-(-2-methylbenzoyl) peroxide (a. mixture of 77.2percent peroxide and 22.8 percent water by weight) were placed inthermostatted chambers held at 30 C. and 40 C. After four (4) weeks, the

ercent'loss of assa eroxid decom osi tion) was oted. During this tii nethe stabihty to r ap1d decomposition was noted as shown below:

' TABLE IV Temp. (C.)fl"ime (Weeks) Loss of Assay (2 results show thatlittle assay is lost at 50 C. in 4 weeks and, even at 40 C., is stableto rapid decomposition.)

What is claimed is:

1. In a process for curing an unsaturated polyester resin composition,said composition comprising (a) an unsaturated polyester selected fromthe esterification product of one or more ethylenically unsaturated diorpoly-carboxylic acids or their anhydrides with one or more saturated orunsaturated polyalcohols, in admixture with (b) an ethylenicallyunsaturated monomer, at curing temperatures in the presence of a curingcatalyst, the improvement which comprises employing

2. A process according to claim 1 wherein said resin compositioncomprises (a) the esterification product of propylene glycol, maleicanhydride and phthalic anhydride in admixture with (b) monomericstyrene.
 3. A process according to claim 1 wherein said curing isaccelerated by the addition of N,N-dimethylaniline.